Heating system for heating the passenger compartment of a motor vehicle

ABSTRACT

The invention relates to a heating system for heating the interior of a motor vehicle, there being a combustion heater ( 10 ) for burning fuel in order to heat the air supplied to the vehicle interior and/or liquid in the vehicle in the cooling circuit of the engine. An electrical heating device ( 20 ) is integrated into the combustion heater ( 10 ) in order to supply heat to the air or liquid to be heated.

[0001] This invention relates to a system for heating the interior of a motor vehicle as claimed in the preamble of claim 1.

[0002] To heat a motor vehicle interior independently of the vehicle engine, conventionally combustion heaters are combined with a conventional heating system which is based on heat exchange with the coolant circuit of the engine. The combustion heater can burn fuel from the vehicle fuel tank in order either to directly heat air which is delivered into the vehicle interior or to heat coolant in the coolant circuit which then delivers heat to the vehicle interior via one or more heat exchangers.

[0003] DE 199 02 050 A1 discloses a heat exchanger which is equipped with an electrical heating device. Heating by means of an electrical heating device, especially with the engine off, is possible only for a very short time since otherwise the vehicle battery is overloaded and restart of the engine is endangered.

[0004] DE 198 57 240 A1 discloses a heater which can be operated both with liquid fuel and also with an electrical heating element in the form of a heating coil which can be integrated into the heat exchanger of the heater. The heating coil must be inserted during installation into the vehicle heater or its heat exchanger and contacts established, a complex procedure. Since in the area of the heating coils a liquid heat exchange medium is circulated, both the heating coil and also its contacts must be provided with waterproof insulation. This greatly increases the costs of one such combined heating device.

[0005] The object of the invention is to devise a motor vehicle heating system with a combustion heater which can be operated as flexibly as possible and still has simple installation, low costs, good efficiency and low installation space requirements.

[0006] This object is achieved as claimed in the invention by a heating system as is defined in claim 1. By integrating an electrical heating device into the combustion heater, the latter can be operated much more flexibly and with higher heat output without significantly increasing the installation space required, the installation requirements, and costs.

[0007] Preferred embodiments of the invention are given in the dependent claims.

[0008] The invention is detailed below using the attached drawing which schematically shows one embodiment of the invention.

[0009] The sole figure schematically shows a combustion heater 10 which is supplied with fuel from the fuel tank of the vehicle to produce combustion heat which is used to heat the coolant from the coolant circuit of the motor vehicle engine. The combustion heater 10 comprises as the heat exchanger a block 12 for feed and discharge of coolant in counterflow by means of a feed channel 14 and a discharge channel 16. The heat exchanger block 12 consists of a material with good thermal conductivity and is in direct thermal contact with the combustion section 18 of the combustion heater 10. On the bottom of the heat exchanger block 12 there is a PTC (positive temperature coefficient) heating element 20 in direct thermal contact with the heat exchanger block 12 in order to heat it if necessary and thus heat the coolant flowing through the heat exchanger block 12 independently of the combustion section 18. For this purpose the PTC heating element is supplied with electricity from the vehicle electrical system, the wiring feasibly being chosen such that the PTC element 20 can only consume electricity when the generator is generating enough power to prevent discharge of the vehicle battery.

[0010] This integration of the PTC heating element 20 into a combustion heater 10 preferably on or in one wall of the heat exchanger block 12 has the advantage that without significant additional installation cost and installation space requirement, more flexible heating of the engine coolant independently of the engine is possible than is the case in a conventional combustion heater. Thus, on the one hand heating of the coolant is possible even with the combustion section 18 turned off, by the PTC heating element 20 being supplied with electricity, while on the other hand when the combustion section 18 is in operation greater heat output is available and thus faster heating of the coolant is possible than would be the case without the additional electrical heating element 20.

[0011] With integration in one wall of the combustion heater 10 or of the heat exchanger block 12, the heating element 20 in the form directly during manufacture, for example when the housing is cast, can be embedded as resistance wires or plates into the corresponding wall. Thus extremely simple production becomes possible. The electrical heating elements are best protected against damage. Calcification is precluded since there is no contact with the liquid heat exchange medium, as in the initially mentioned DE 198 57 240 A1. Outstanding heat transfer from the heating elements 20 to the respective wall is ensured.

[0012] In an arrangement from outside on one wall of the combustion heater 10 or the heat exchanger block 12 the electrical heating element 20 is advantageously covered in addition to the outside by a heat insulating layer or foil in order not to have to tolerate major radiation losses to the outside. 

1. Heating system for heating the interior of a motor vehicle, with a combustion heater (10) for burning fuel in a heat exchanger in order to heat the air supplied to the vehicle interior and/or liquid in the vehicle in the cooling circuit of the engine, characterized in that an electrical heating device (20) is integrated on or in one wall of the combustion heater (10) in order to supply heat to the air or liquid to be heated.
 2. Heating system as claimed in claim 1, wherein the combustion heater (10) comprises a heat exchanger block (12) for feed and discharge of liquid in counterflow, the heating device (20) being in direct thermal contact with the heat exchanger block (12) in order to heat it.
 3. Heating system as claimed in claim 2, wherein the heating device (20) is located on the outside of the heat exchanger block (12).
 4. Heating system as claimed in claim 2, wherein the heating device (20) is integrated into one wall of the heat exchanger block (12).
 5. Heating system as claimed in one of the preceding claims, wherein the heating device (20) is one or more PTC heating elements.
 6. Heating system as claimed in one of the preceding claims, wherein the heating device (20) is supplied from the vehicle electrical system. 